When depositing a web, e.g., from the supporting arms of a web changer onto a shifting platform, relatively high forces may arise, which may lead to a destruction of parts of the web changer or of the shifting platform. As an example, FIG. 1 shows a web changer 1, which holds webs of paper 6 and 7 via the supporting pins 1a and 1b. To change a web of paper, e.g., a full web of paper 6 is brought to the web changer 1 via a shifting platform 3 and is picked up by the web changer 1 and is pivoted by means of the supporting pin 1a, whereby a web 7, which is to be changed and is, e.g., almost completely unwound, is again deposited on the shifting platform 3. If the angle w during the depositing and removal from the axle of this web of paper 6 on the holding device 5 of the shifting platform 3 is relatively small and lies, e.g., in the range of 0 to 15 degrees, then forces may arise which would destroy parts of the web changer 1 as well as of the shifting platform, especially if the shifting platform 3 is not spring-loaded and the drive motor of the supporting arm 2 pivots with a large torque.
A web changer, with which a web of paper can be unloaded via a shifting platform, is known from DE 43 34 582 A1. With this, a measuring device is needed in the web changer, with which the web velocity of the web of paper running off and the angular velocity of the web of paper, from which this web is unwound, can be measured, so that the diameter of the web of paper can be determined as a quotient of the web velocity and the angular velocity, from which the angle and the distance, under which the shifting platform picks up the web of paper, are determined.
DE 197 14 551 C2 describes a device for removing a web of printed matter from supporting arms of a web changer in a web-fed printing press with a holding device, onto which the web of printed matter can be deposited, whereby on the holding device there is provided a pressure sensor for detecting the weight and pressure exerted by the web of printed matter and the supporting arms on the holding device. A calculation setup of a control circuit determines the difference between an actual pressure value detected by the pressure sensor and a residual web pressure value of the web of printed matter to be changed, which was calculated or predetermined beforehand. The lowering of the supporting arms is stopped via the control circuit, if the pressure which is applied to the holding device within a predetermined bandwidth corresponds to the amount of the weight of the web of printed matter to be deposited, whereupon the tensioning spindles of the supporting arms, released by the weight of the web of printed matter, can be pulled out.
However, if no or false signals are issued by a measuring instrument or such a pressure sensor, since no reliable information is present, e.g., because of a web tear or emergency switching off, then there may yet be high reaction forces on the shifting platform when removing a web of printed matter, as a result of which, on the one hand, parts of the web changer and, on the other hand, the shifting platform may be damaged or even destroyed.